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1. Be in contradiction with
   - contradict, belie
    
2. Deny the truth of
   - contradict, contravene
    
3. (logic) prove negative; show to be false
   - contradict
    
4. Make ineffective by counterbalancing the effect of
   "This action will negate the effect of my efforts";
   - neutralize, neutralise [Brit], nullify

Derived forms: negating, negated, negates

Type of: demonstrate, depart, deviate, differ, disagree, dissent, diverge, establish, prove, shew [Brit, archaic], show, take issue, vary, weaken

Antonym: support

Encyclopedia: Negate